Hydrogen or helium would decrease the density, but I digress. In most cases, composites have complementary materials. You would need less titanium if it was re

Hydrogen or helium would decrease the density, but I digress. In most cases, composites have complementary materials. You would need less titanium if it was reinforced with something else. Examples: - Most common are materials like carbon fiber, ceramic, or aramid. - Another failure mode is denting (or localized impact damage). If I make a tube, as here, the thinner the wall and wider the radius, the stronger it is as a unit. However, at some point, it's easy to crush it like an aluminium can. Cover the inside with a polyurethane foam, and that failure mode goes away, or at least dramatically decreases, for very little added weight. - I might care about things like thermals. Etc.